1. Field of the Invention
This invention relates to an automobile weight sensor for detecting the presence of a person having a weight in a car seat, and in particular to a sensor that can detect the presence of an occupant using strain sensitive resistors and provide an electrical signal to control activation of an airbag.
2. Description of the Related Art
Various devices are well known for their ability to measure force, pressure, acceleration, temperature, position, etc. by using a sensing structure combined with signal processing electronics. One general type of sensor or transducer for such applications is a resistive strain gauge sensor in which force or pressure is sensed or measured based on strain placed on the resistors. Resistive strain gauges function by exhibiting changes in resistance in response to strain in the resistor.
Many types of strain gauge sensors have been designed and made commercially available. Various strain gauge sensors have proven to be generally satisfactory. Prior art sensors, however, have tended to be rather expensive and not suitable in certain applications such as sensing the presence of an occupant in an automobile seat. A sensor suitable for such an application must be compact, robust, impervious to shock, vibration and enviornmental contaminants and yet inexpensive.
Automobile seats can use sensors to activate air bags, which would be deployed during an accident. Injury to infants or small children from air bag deployment with excessive force is a current industry problem. A weight sensor in the seat can be used to control the deployment force during air bag activation. If a heavy person is in the seat, the airbag is deployed at full force. If a light person is in the seat, such as a child, the airbag is deployed at a slower, less forceful rate or not at all.
A problem with the sensor of U.S. patent application Ser. No. 09/422,382 is that during manufacturing it requires several processing steps. For example, the resistor pattern can only be screened on one side of the substrate and dried at a time. The substrate is screened and cured on one side then inverted to screen the resistors on the other side and then cured again, adding to processing time.
A current unmet need exists for a reliable, low cost, simple and robust automobile weight sensor that is easily manufacturable.
It is a feature of the invention to provide a reliable and cost-effective weight sensor for detecting applied weight. The sensor is useful in measuring the weight of a vehicle seat occupant. The sensor uses strain sensitive resistors.
An additional feature of the invention is to provide a weight sensor for sensing an applied weight. The sensor includes a first and second outer substrate that have a first and second end and an inner surface and an outer surface. An inner substrate has a first and second end. The first and second outer substrates and the inner substrate are fixedly attached together. Several strain gauge resistors are located on the outer surfaces of the first and second outer substrates to generate an electrical signal in response to the substrate being stressed by the applied weight. The electrical signal changes as a function of the applied weight. The substrate has a neckdown region located between the first and second ends for concentrating the applied weight. The strain gauge resistors are located in the neckdown region.
The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed and it is distinguished from the prior art in this particular combination of all of its structures for the functions specified. Other features of the present invention will become more clear from the following detailed description of the invention, taken in conjunction with the accompanying drawings and claims.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.